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Documented the new invokable event listeners #9281

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Documented the new invokable event listeners
javiereguiluz Feb 16, 2018
1666cbd
Added the versionadded directive
javiereguiluz Feb 16, 2018
f78528b
Typo
javiereguiluz Feb 18, 2018
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34 changes: 23 additions & 11 deletions event_dispatcher.rst
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Expand Up @@ -107,19 +107,31 @@ using a special "tag":
->addTag('kernel.event_listener', array('event' => 'kernel.exception'))
;

Symfony follows this logic to decide which method to execute inside the event
listener class:

#. If the ``kernel.event_listener`` tag defines the ``method`` attribute, that's
the name of the method to be executed;
#. If no ``method`` attribute is defined, try to execute the method whose name
is ``on`` + "camel-cased event name" (e.g. ``onKernelException()`` method for
the ``kernel.exception`` event);
#. If that method is not defined either, try to execute the ``__invoke()`` magic
method (which makes event listeners invokable);
#. If the ``_invoke()`` method is not defined either, throw an exception.

.. versionadded:: 4.1
The support of the ``__invoke()`` method to create invokable event listeners
was introduced in Symfony 4.1.

.. note::

There is an optional tag attribute called ``method`` which defines which method
to execute when the event is triggered. By default the name of the method is
``on`` + "camel-cased event name". If the event is ``kernel.exception`` the
method executed by default is ``onKernelException()``.

The other optional tag attribute is called ``priority``, which defaults to
``0`` and it controls the order in which listeners are executed (the highest
the priority, the earlier a listener is executed). This is useful when you
need to guarantee that one listener is executed before another. The priorities
of the internal Symfony listeners usually range from ``-255`` to ``255`` but
your own listeners can use any positive or negative integer.
There is an optional attribute for the ``kernel.event_listener`` tag called
``priority``, which defaults to ``0`` and it controls the order in which
listeners are executed (the highest the priority, the earlier a listener is
executed). This is useful when you need to guarantee that one listener is
executed before another. The priorities of the internal Symfony listeners
usually range from ``-255`` to ``255`` but your own listeners can use any
positive or negative integer.

.. _events-subscriber:

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